Rubber radial bearing

ABSTRACT

In a sleevelike hydraulically damping rubber bearing with at least two hydraulic working chambers, at least one throttle duct for the damping of vibrations of low amplitudes and one bypass duct for opening the bearing for shock amplitudes are provided. In order to improve the impermeability of the bearing to low disturbing noises, the natural resonance, typically located in the subacoustic range for such bearings, can be shifted into a frequency range around 200 Hz by the insertion of an uncoupling element.

The invention relates to a hydraulically damping sleevelike rubberbearing.

The invention accordingly relates, in particular therefore, to ahydraulically damping sleevelike rubber bearing, especially radialrubber bearing, with different spring characteristics (F1, F2) radiallyperpendicular to one another. The bearing consists of an innersleevelike connecting block (1) and of a likewise sleevelike cage (2)surrounding the latter, said block and said cage, lying axially parallelone in the other, being vulcanized or otherwise embedded in a rubberspring block (3). At least two diametrically opposed pumping workingchambers (4, 5) for a working fluid, communicating with one another viaat least two overflow ducts (6; 21), are designed in the rubber springblock (3) in such a way that said working chambers are closed off in afluid-tight manner, radially relative to the outside, by the cylindricalinner wall (7) of an outer sleeve (8), for which purpose the rubberspring block (3), reinforced by the cage, is pressed under radialprestress into the outer sleeve (8). The at least two overflow ductshave permeability behaviors and damping behaviors which are differentfrom one another and are in each case tuned to different amplituderanges.

Such a sleeve bearing is known from European preliminary publication EP0 335 007 A2. It has a throttle duct of small cross section for dampingof vibrations of relatively low amplitudes, particularly of the order ofmagnitude of ±0.1 mm in the acoustic frequency range of approximately 40to 200 Hz, and a second overflow duct of larger cross section, whichacts as a bypass duct for this throttle duct, in which a rubber lip isprovided as a bypass valve. When excessively high amplitudes (>±2 mm)act on the bearing, that is to say when a pressure gradient, increasedbeyond the intended operating characteristic data foreseeable for therespective use of the bearing, occurs in one of the two fluid chambers,the rubber lip opens and allows damping fluid to overflow from onechamber to the other in each case, the pressure gradient at the sametime being compensated, and, if appropriate, with slight damping.

The phenomena mentioned, which act with excessively high amplitudes onthe bearing, are, particularly in the field of motor vehicle technology,as a rule, either stochastic shocks and impacts or low frequencyvibration-like phenomena of high amplitude, occur, for example, in themotor vehicle when it travels over undulating roads of long wavelengthand, as a rule, are at frequencies of below 10 Hz, that is to say atfrequencies well into the subacoustic range.

So that the forces which occur during these dynamic spring loads, andwhich are sometimes very considerable, can be absorbed both inconformity with the appropriate function and with as much care aspossible being taken of the material of the rubber spring, bearings ofthis type are conventionally tuned in such a way that their fundamentalresonance is placed in the range between 10 and 30 Hz, that is to say inthe range between the markedly subacoustic frequencies and the lowestacoustic frequencies. For this purpose, however, it is necessary, in thecase of bearings of this type, to allow for the fact that, after theresonance maximum, the dynamic spring constant of the bearing scarcelydecreases appreciably toward higher frequencies. However, the higher thedynamic bearing spring constant remaining after the resonance maximum,the more permeable the bearing becomes to a passage of subsequentfrequencies in the acoustic range, so that disturbing acousticvibrations, taking the form of only insufficiently damped or evenvirtually undamped solidborne sound, pass through from the supportingconnection to the abutment connection, that is to say from the innersleeve to the outer sleeve or, conversely, from the outer sleeve to theinner sleeve of the rubber sleeve bearing. When such sleeve springs areused in motor vehicle construction, this leads to the acousticdiscomfort in the motor vehicle being impaired to an extent which cannotbe ignored.

Proceeding from this state of the art, the technical problem on whichthe invention is based is to improve a hydraulically damping sleevelikerubber bearing of the type explained above, to the effect that, after asubacoustic damping range, that is to say a frequency range of belowapproximately 10 Hz and a resonance maximum in the range of 10 to 30 Hz,the sleeve spring has, in the subsequent low acoustic frequency range atleast up to a range of approximately 200 Hz, a markedly reduced dynamicbearing spring constant, as compared with the state of the art, in orderto suppress the transmission of solidborne sound in this lower acousticrange.

The invention achieves this object in, that a transmission of vibrationsof low amplitude through the bearing is brought about not only bythrottle losses in a flow of the working fluid in a throttle duct, butessentially also due to the fact that the supporting connection pieceand the abutment connection piece of the sleeve bearing are acousticallyuncoupled by means of an uncoupling member.

In this case, uncoupling is carried out, in a way known per se forlarge-volume supporting bearings, via a loose piece which makes itpossible to compensate the sound pressure between the fluid chambers ofsuch a supporting bearing, without relevant displacements in the volumeof the damping fluid occurring in the throttle duct between the workingchamber and compensating chamber. In this case, the loose piece isarranged in a separate subsidiary duct to the throttle duct.

In the sleeve bearing under consideration here, the flutterable loosepiece serving as an uncoupling member is arranged in one of the twooverflow ducts of the sleeve bearing, that is to say either in thedamping duct or, preferably, in the bypass duct. In this case, “Loosepiece” means, in the usual sense, an insert part which is inserted orreceived in a receptacle or cage loosely, that is to say without anypositive connection, so as to be limited on all sides, but freelymovable within this framework, and flutterable.

If the restraint for the loose piece is designed as a cage, the wallperforations of such an uncoupling cage must have such large dimensionsthat they allow a throttle-free passage of the solidborne sound waves oflow amplitudes which are to be uncoupled in the damping fluid of thesleeve bearing.

However, since, under some circumstances, the use of cages forrestraining the loose piece when the bearing is subjected to shocks maynot be entirely without its problems, the loose piece inserted in thesleeve bearing of the invention is preferably mounted flutterably inundercut structures (FIG. 3).

The material of the loose piece itself may, in principle, be selected,as desired, from materials of relatively low density, that is to saymay, for example, also be a plastic part or an aluminum sheet, but, forthe present purpose, is preferably an elastomeric part, in particular anelastomeric web or an elastomeric diaphragm, in order to rule out theoccurrence of rattling noises or fluttering noises of the loose piece,in particular in a cage.

According to a preferred embodiment of the invention, the uncouplingmember is oriented axially parallel to the longitudinal axis of thesleeve spring and extends preferably over the axial width of the rubberspring body between two end-face sealing means, preferably twocylindrical surface sealing rings of the sleeve cage of the rubberspring. This design makes it possible, if the uncoupling member has onlya small overall height in the radial direction of the sleeve spring,nevertheless to provide an effective surface which is sufficiently largefor acoustic uncoupling.

If a cylindrical surface seal is used on the two end faces of the sleevespring, the throttle duct is designed preferably in the radially outergenerated surfaces of the cylindrical rings. The two part throttle ductsthus designed are connected communicatingly, again with respect to thesleeve bearing, by means of a duct portion axially connecting the twoend-face annular ducts to one another. If the uncoupling member isarranged in the throttle duct, it is then preferably arranged in thisaxially running connecting portion.

Instead of a decoupling cage with an inserted loose piece, especially anelastomeric diaphragm as a loose piece, other means known per se mayalso be used for acoustic uncoupling, above all an easily deformablerubber diaphragm or rubber lip which either can be designed in one piecewith the rubber spring block or can be fastened or movably secured inanother way in the bypass duct or in the throttle duct.

If the hydraulically damping sleevelike rubber bearing is equipped witha bypass duct, the uncoupling of the acoustic vibrations of lowamplitudes preferably takes place at or in such a bypass duct, in whichcase, however, such uncoupling must then be arranged, in functionalterms, not in series with the bypass duct valve, but parallel to thelatter, in order not to impair the damping fluid stream which, asintended, occurs in this bypass duct under shocks which act on therubber bearing. Both functionalities, namely permeability to pressureshocks in the damping fluid and the uncoupling of acoustic vibrationswith low amplitudes, must be implemented in such a way that they areavailable in the sleeve bearing independently of one another infunctional terms and without impairing one another. Such a functionalparallelism of the bypass valve and the uncoupling member does not,however, rule out the possibility of both functions also beingimplemented in one and the same structural part, since they must respondat limit values of the pressure fluctuations occurring in the dampingfluid, these limit values being markedly different in each case.

The rubber sleeve bearing of the invention is preferably used as aradial bearing. It may, however, likewise be employed effectively foruse as an axial bearing, specifically, in particular, when such an axialbearing is also exposed to relatively high radial forces during itsintended use.

The invention is explained in more detail below with reference toexemplary embodiments, in conjunction with the drawings,in which:

FIG. 1 shows, in radial section, an exemplary embodiment of ahydraulically damping sleevelike radial rubber bearing with anuncoupling member designed as a cage and loose piece;

FIG. 2 shows bearing spring characteristics for the exemplary embodimentshown in FIG. 1 and for a comparative bearing according to the state ofthe art; and

FIG. 3 shows a perspective part illustration of a combined bypassvalve/uncoupling member in a bypass duct to a sleeve spring.

FIG. 1 illustrates, in radial section, a hydraulically damping rubbersleeve spring with an uncoupling element for the uncoupling of lowfrequency acoustic vibrations.

An inner sleevelike or hublike connecting block 1 is surrounded in anaxially parallel manner by a sleevelike cage 2. The inner connectingblock 1 and the sleevelike cage 2 are vulcanized into a rubber springblock 3. Two working fluid chambers 4, 5 are designed in the rubberspring block 3 and communicate with one another via the two branches 6′,6″ of a throttle duct 6. The working chambers 4, 5 and the throttle duct6 are closed off in a fluid-tight manner, radially relative to theoutside, by means of the cylindrically inner wall 7 of an outer sleeve 8made of steel. For this purpose, the rubber spring block 3, reinforcedby the sleeve cage 2, is pressed under radial prestress into the outersleeve 8. A bypass duct of larger cross section, which is notillustrated here, is designed radially opposite the throttle duct 6 (inthe lower portion of FIG. 1 which is not shown).

The sleeve spring has a softer spring characteristic in the radialworking direction, illustrated by the double arrow F1, than in thetransverse direction which is oriented perpendicularly to the latter inthe radial plane and which is characterized by the double arrow F2.

Inserted in the course of the throttle duct 6, which connects thechambers 4, 5 to one another, is an uncoupling member 9 which consistsof an uncoupling cage 10 and of an inserted loose piece 11 in the formof an elastomeric diaphragm. At the same time, the two mutually oppositewalls 10 of the uncoupling member 9 extend, axially parallel to thebearing longitudinal axis, over the entire axial length of the workingchambers 4, 5 and of the ducts designed axially laterally of thechambers. A series of bores 12 lying closely next to one another isdesigned in each of the cage walls. Inserted between the two uncouplingchamber walls 10 which form a cage is a self-supporting elastomericstrip 11 which, at most loosely, bears with all its side surfaces on thesurrounding wall surfaces of the uncoupling chamber. As is clear fromFIG. 1, the thickness of the elastomeric strip is markedly smaller thanthe clear distance between the two inner wall surfaces of the uncouplingchamber walls 10.

When vibrations of low amplitudes, that is to say vibrations ofamplitudes in the range of <±0.1 mm, are introduced into the connectingblock 1, they pass as solidborne sound vibrations, via the connectingblock 1, into the pressure fluid of the working chambers 4, 5 and run aspressure waves through the working fluid out of the working chambers 4,5, through connecting apertures not illustrated in FIG. 1, into thethrottle part ducts 6′, 6″ , through these and through the bores 12 tothe elastomeric loose piece 11 in the uncoupling member 9. Since theworking chambers 4, 5 and the pressure wave paths through the apertures,not illustrated, and via the throttle duct portions 6′ and 6″ aredesigned to be essentially symmetric under load, the sound pressurewaves impinge, in a way complementary to their generation, onto theelastomeric loose piece in the uncoupling member, where they arecanceled, virtually unreflected, without damping processes or flowprocesses occurring in the throttle duct 6. A bypass duct remainsunaffected by this event.

It should be pointed out, in this respect, that a radial rubber sleevebearing is illustrated in FIG. 1 in the uninstalled unloaded state, inwhich the longitudinal axis 17 of the bore 18 in the inner connectingblock 1 does not run coaxially, but merely axially parallel to thebearing axis 19 and to the longitudinal axis 20 of the sleeve (2). Inthis case, in the state shown in FIG. 1, before an intended installationof the bearing, the rubber spring body 3 is configured and prestressedin such a way that, under the action of the predetermined static nominalload on the connecting block, from left to right in the direction of thedouble arrow F1 in the illustration of FIG. 1, the rubber spring 3 isdeformed to such an extent that all three axes (17, 19, 20) mentionedthen actually coincide coaxially at the zero point of an exerted dynamicload.

The action of the uncoupling member 9 shown in FIG. 1 may be gatheredfrom the sleeve spring bearing characteristics shown in FIG. 2.

The curve 13 shows the profile of the dynamic spring constant as afunction of the frequency of a vibration imparted to the connectionpiece, through the sleeve spring according to the prior art without anuncoupling member. The resonance of the throttle duct, which is in therange around 40 Hz, and the high dynamic rigidity of the sleeve springaccording to the prior art, which remains above approximately 40 to 50Hz, can be seen clearly.

In FIG. 2, the curve 14 shows the associated loss angle, likewise as afunction of the load frequency.

The curve 15 of FIG. 2, provided with the measurement points, shows theprofile of the dynamic spring constant to the same sleeve spring afterthe uncoupling member 9, illustrated in FIG. 1, has been installed. Thesleeve bearing according to the invention reaches the dynamic springconstant only at a frequency of above 200 Hz, this constant alreadyoccurring from 50 Hz for the bearing according to the prior art. Thus,whilst, in bearings according to the prior art, the entire acousticdisturbance vibration range from above approximately 40 to 50 Hz runs assolidborne sound through the bearing from the inner connecting block asfar as the outer connection sleeve, in the bearing of the invention itis possible, above all, to uncouple the acoustic disturbance range, inthe frequency range of up to 200 Hz, which presents problems in motorvehicle construction.

The frequency profile, belonging to curve the 15 in the graph of FIG. 2,of the loss angle for the sleeve bearing according to the invention isreproduced in the curve 16.

FIG. 3 shows a perspective part view, partly in radial section, of asecond exemplary embodiment of the invention.

FIG. 3, taken in radial section, shows a portion of a bypass duct (21),which ensures permeability of the sleeve bearing to pressure shockswhich may occur in the damping fluid.

The inner cage 2, which consists of steel, has, on the end faces, twocylindrical annular portions 2′ which are connected to one another viaaxially running webs 2″ so as to form the cage 2 for the rubber spring3. As also illustrated here in FIG. 3, the entire surface of the cage 2is provided, overall, with a highly absorbent and damping rubberizinglayer 3′ which is produced together with the rubber spring 3 as anintegral part of the latter. Otherwise, the sleeve bearing, a detail ofwhich is illustrated in FIG. 3, is, in principle, designed in the sameway as the exemplary embodiment shown in FIG. 1, so that details are notillustrated in FIG. 3.

By pushing over the outer steel sleeve 8 (FIG. 1), the ducts andrecesses of the sleeve body are closed in a fluid-tight manner. At thesame time, the bypass duct 21 reducing the pressure shocks in thedamping fluid is closed relative to the outside via the cylindricalsurface 22 which, in the way likewise made clear in FIG. 1, forms acylindrical surface seal relative to the inner wall 7 of the outersleeve 8 (FIG. 1).

Recesses 25 for receiving an insert part 26 are provided in thecylindrical bottom surface 23 as well as in the annular side wall 24 andin the cylindrical sealing surface 22 of the rubberized bearing springsleeve 2. The insert part 26 consists of metal or plastic and has acuboid or parallelepipedic configuration at its ends located axiallyopposite one another. These two end parallelepipeds 27 located axiallyopposite one another are connected to one another by means of a flatcarrier rail 28.

A weblike sealing lip 29, tapering radially outward, is arranged on thecarrier rail 28 of the insert part 26 so as to be fixedly connected to asaid carrier rail. The radial height of this sealing lip 29, relative tothe sleeve bearing, is dimensioned in such a way that, in the assembledbearing, said sealing lip just avoids touching the inner wall 7 of theouter sleeve 8. The radially outer top edge of the sealing lip 29 leavesa free gap of ≈0.1 mm, with a tolerance of −0.1 mm, relative to theinner wall surface 7 of the outer sleeve 8.

The recess 25 is dimensioned, overall, in such a way that the entireinsert part 26 inserted into the recess 25 has all round, butparticularly in the tangential direction, a movability which, althoughlimited, is nevertheless sufficient to ensure that it can act in the waydescribed above as a loose piece for acoustic vibration uncoupling. Atthe same time, as regards the choice of material, this loose piece isheld so as to be movable so easily and with such low friction that, whenacoustic pressure waves impinge on to its surfaces located transverselyopposite one another in the bypass duct, it can flutter in anacoustically uncoupling manner in the way indicated by the double arrow30 in FIG. 3.

At the same time, the two radially outwardly pointing surfaces 31 of theparallelepipedic end parts 27 of the insert part 26, said surfaces beinglocated axially opposite one another on the cage web 28, aredimensioned, in their radial vertical position, with such undersize inrelation to the inner surface 7 of the outer sleeve 8 (FIG. 1) that,under comparatively high pressure shocks in the damping fluid of thebearing which act on the web 29, said surfaces can be tiltedsufficiently far to be capable of acting as a bypass valve body and ofopening, that is to say to be permeable to shock waves and highamplitudes.

The insert part 26 arranged transversely in the bypass duct 21 thusperforms both the function of a loose piece for the uncoupling ofacoustic vibrations and the function of a valve body for thepermeability of the sleeve bearing to high amplitudes and shock fronts.

By virtue of their characteristic data, in conjunction with their smalloverall size, the sleevelike radial rubber bearings according to theinvention are used preferably in motor vehicle construction as a chassisbush, in particular for reducing transverse axle vibrations on the crossstruts of the vehicle front axles.

What is claimed is:
 1. A hydraulically damping sleeve bearing,comprising: an outer sleeve; an intermediate cage surrounded by saidouter sleeve; an inner connecting block surrounded by said intermediatecage, said inner block and intermediate cage being embedded in anelastomer spring body; said spring body being shaped to form, togetherwith an inner wall of said outer sleeve, at least two working chamberscommunicating with each other via at least one damping throttle duct andat least one bypass duct, said throttle and bypass ducts havingdifferent dynamic characteristics and being tuned to different frequencyand amplitude ranges; said working chambers, and said throttle andbypass ducts being filled with a damping fluid sealed off in afluid-tight manner; said bypass duct including a decoupling member fordecoupling said damping fluid between said working chambers in responseto low amplitude vibrations, and a pressure relief valve for openingsaid bypass duct in response to high amplitude vibrations and pressurefronts occurring in said damping fluid, wherein said decoupling memberand pressure relief valve are integrated into a single functional unitformed as a loose piece without any positive connection.
 2. Thehydraulically damping sleeve bearing according to claim 1, wherein saidinner block and intermediate cage are positioned coaxially in a workingdirection of said sleeve bearing, while said functional unit extendsdiametrically, substantially perpendicularly with said workingdirection.
 3. A hydraulically damping sleeve bearing, comprising: anouter sleeve; an intermediate cage surrounded by said outer sleeve; aninner connecting block surrounded by said intermediate cage, said innerblock and intermediate cage being embedded in an elastomer spring body;said spring body being shaped to form, together with an inner wall ofsaid outer sleeve, at least two working chambers communicating with eachother via at least one damping throttle duct and at least one bypassduct, said throttle and bypass ducts having different dynamiccharacteristics and being tuned to different frequency and amplituderanges; said working chambers, and said throttle and bypass ducts beingfilled with a damping fluid sealed off in a fluid-tight manner; saidbypass duct including a decoupling member for decoupling said dampingfluid between said working chambers in response to low amplitudevibrations, and a pressure relief valve for opening said bypass duct inresponse to high amplitude vibrations and pressure fronts occurring insaid damping fluid, wherein said decoupling member and pressure reliefvalve are integrated into a single functional unit; wherein saidfunctional unit comprises a tiltable tip valve mounted as a loose piece,across said bypass duct so that said tip valve is displaceable alongsaid bypass duct in a flutterable manner under said low amplitudevibrations, and tiltable sufficiently far to open said bypass duct undersaid high amplitude vibrations or pressure fronts.
 4. The hydraulicallydamping sleeve bearing according to claim 3, wherein said functionalunit further comprises at least an insert part fixedly connected withsaid lip valve and loosely held in a recess formed in a wall of saidbypass duct; a clearance between said insert part and said recess ismade so that said insert part is displaceable along said bypass duct ina flutterable manner under said low amplitude vibrations, and tiltablesufficiently far under said high amplitude vibrations or pressurefronts.
 5. The hydraulically damping sleeve bearing according to claim3, wherein a cross section of said bypass duct is larger than a crosssection of said throttle duct.
 6. A chassis bush of a motor vehicleusing a hydraulically damping sleeve bearing, said sleeve bearingcomprising: an outer sleeve; an intermediate cage surrounded by saidouter sleeve; an inner connecting block surrounded by said intermediatecage, said inner block and intermediate cage being embedded in anelastomer spring body; said spring body being shaped to form, togetherwith an inner wall of said outer sleeve, at least two working chamberscommunicating with each other via at least one damping throttle duct andat least one bypass duct, said throttle and bypass ducts havingdifferent dynamic characteristics and being tuned to different frequencyand amplitude ranges; said working chambers, and said throttle andbypass ducts being filled with a damping fluid sealed off in afluid-tight maimer; said bypass duct including a decoupling member fordecoupling said damping fluid between said working chambers in responseto low amplitude vibrations, and a pressure relief valve for openingsaid bypass duct in response to high amplitude vibrations and pressurefronts occurring in said damping fluid, wherein said decoupling memberand pressure relief valve are integrated into a single functional unitformed as a loose piece without any positive connection.